This invention relates to a guide rail and a method of forming the guide rail in a sliding roof apparatus, which is arranged around an opening provided on the roof of an automobile, in order to open or close the opening in the roof. In vehicles having a sunroof, a mechanism is typically installed for opening and closing the opening by a manually operated or motor-driven sliding panel. The popularity of sunroofs is generally attributed to the fact that sunroofs are considered to provide the occupants of the vehicle with a feeling of space openness, while furnishing the passenger compartment with excellent ventilation.
The mechanism for opening and closing the roof panel opening by the sliding panel includes a square housing, which has a centrally located opening, secured to the periphery of the opening in the roof panel of the automobile. A guide rail is secured to the left, right, and front (or rear) sides of the housing, end is driven by an electric motor attached to the front or rear portion of the housing. A pair of shoes are accommodated in the guide rail. The shoes are connected to the sliding panel via links having cam grooves, and are further connected to the electric motor via drive cables.
The sliding panel is so adapted that when an occupant of the automobile switches on the electric motor to open the panel, the motor is driven into operation and pulls the shoes backwardly to raise the sliding panel about its leading edge, thereby causing the sliding panel to be tilted upwardly. This position can be maintained for some time with the motor being left switched on. An occupant who desires the up-tilted state switches off the motor at this time.
If the occupant wishes to retract the sliding panel to uncover the opening in the roof panel, the electric motor is switched on, whereupon the electric motor is again driven into operation to retract the upwardly tilted sliding panel and uncover the opening in the roof panel, thereby exposing the interior of the passenger compartment to the outside. To close the opening, the electric motor is switched on in the closing direction, whereby the sliding panel is made to perform an operation which is the reverse of the foregoing.
The guide rail of this sliding roof apparatus comprises two parallel portions situated on the lower side of the sliding panel and on both the sides of the housing. The parallel portions, which extend longitudinally along the vehicle, slidably support the shoes of the sliding panel. The guide rail also includes a connecting portion extending between the front ends of the parallel portions of the rail, thereby forming a generally U-shaped configuration. An aluminum alloy exhibiting little expansion and contraction and a low specific gravity preferably mainly is used as the material for the guide rail.
As for the method of bending the guide rail, both ends of an extrusion-molded elongated bar are chucked by respective cylinders adopting, as a neutral axis, the inner peripheral side of the bar that is to be bent. The portion of the bar to be bent on neutral axis is supported on a jig. Then, the cylinders are moved along respective arcs with the point of contact between the jig and the inner peripheral side of the bar or the guide rail serving as a fulcrum, thereby bending the bar or the rail. This completes the bending work.
The guide rail bent by this conventional bending method will not expand or contract at the inner peripheral side, which is the neutral axis. However, since elongation in the longitudinal direction is required on the outer peripheral side and the width of the guide rail is relatively large, the bent portion of the guide rail cannot be made with a small radius. Such elongation is proportional to the distance between the inner peripheral side, which is the neutral axis, and the outer peripheral side. The amount of required elongation increases in proportion to this distance.
Accordingly, when an effort is made to provide a small radius in order to obtain a large effective opening in the sliding roof apparatus, the guide rail breaks on its outer peripheral side. As such, in conventional sliding roofs, bending is, limited to an outer-periphery radius/inner-periphery radius ratio of 1.5.
With a guide rail having a large radius, the guide rail will bite into both ends at the front of the opening of the sliding roof apparatus, as a result of which a large effective opening cannot be obtained.
The guide rail mentioned above can be provided with a center frame. An example of such an arrangement is disclosed in the specification of Japanese Utility Model Application Laid-Open (KOKAI) No. 57-24120. This prior-art guide rail has a center frame connecting substantially central parts of the above-mentioned parallel portions and extending in the transverse direction of the automobile. The end portions of the center frame are fixedly secured to the lower surfaces of the parallel portions of the guide rail.
It is necessary for the center frame to reinforce the guide rail against externally applied forces. The conventional center frame acts as a guiderail reinforcing member with regard to torsion. However, since the center frame is fixedly secured to the lower surfaces of the parallel portions of the guide rail, it cannot provide reinforcement against external force applied in the vertical direction. In a sliding roof apparatus having a guide rail with such a structure, the panel is subjected to suction due to a pressure difference between the passenger compartment and the roof of the automobile at high-speed travel, and vibration is produced when the vehicle is traveling. As a result, the parallel portions and both end portions of the center frame experience deformation and the sliding roof apparatus will no longer operate smoothly.